Abstract C049: Identification of novel K-Ras G12C inhibitors using a DNA encoded library platform

Abstract

Abstract K-Ras is the most frequently mutated oncogene in cancer. Most mutations cluster in codons 12, 13 and 61, and are involved in the development and progression of a wide range of cancers. Drugging K-Ras has been challenging using traditional drug discovery strategies. Covalent inhibition is a viable drug discovery strategy for drugging difficult targets where identification of non-covalent small molecule inhibitors has been challenging. Marketed covalent inhibitors have been identified for various targets including EGFR and BTK. The K-Ras G12C mutation accounts for 12% of all observed K-Ras mutations in cancer and is most prevalent in non-small lung (NSCLC), pancreatic and colorectal cancers. It has recently been shown that this mutated cysteine can be harnessed for the development of specific covalent inhibitors. We performed covalent based-selections for K-Ras G12C utilizing a 1011 member covalent DNA-encoded library. These selections led to the identification of three novel and chemically distinct series of K-Ras G12C-GDP specific covalent inhibitors. Direct target engagement was demonstrated using FAM-labeled probes in cells over-expressing G12C K-Ras. No target engagement was observed with wild-type or other mutants of K-Ras indicating that these compounds are selective for G12C. Co-crystal structures for all 3 series have been obtained validating the covalent linkage to G12C and also demonstrating “series specific” binding modes for all 3 series of inhibitors. Hit to lead efforts have led us to a tool compound, X-498, which is potent and mutant selective inhibitor of K-Ras G12C. X-498 has a biochemical potency <10 nM (2h) in an HTRF based assay and demonstrates a dose dependent inhibition of phospho-ERK (pERK) in the NCI-H358 (G12C) NSCLC cell line after 4h of compound treatment. No effect on pERK is seen in a G12S containing NSCLC (A549) cell line. In vitro cellular viability assessment of X-498 in K-Ras G12C and non-G12C cancer cell lines demonstrate mutant specific killing of cell lines harboring a K-Ras G12C mutation with GI50 <50 nM and a >400-fold selectivity over a wild-type K-Ras cell line. Structure based drug design is currently being used to optimize chemical properties and potency. Assessment of ADME and PK is ongoing. In summary, we have identified novel chemical series selectively targeting K-Ras G12C mutant that are currently being optimized with the goal of developing treatment for cancer patients harboring the K-Ras G12C mutation. Citation Format: Shilpi Arora, Chris Hupp, Sarah Talcott, Usha Narayanan, Diana Gikunju, Mortiz Von Rechenberg, Michael I Monteiro, John P Giulinger, Kyle Denton, Matt Clark, Andrew Ferguson, Andrew J McRiner, John Cuozzo, Christelle Huguet, Anthony D Keefe. Identification of novel K-Ras G12C inhibitors using a DNA encoded library platform [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C049. doi:10.1158/1535-7163.TARG-19-C049